1. Field of the Invention
The present invention relates to a discharged sheet stacking apparatus in which imaged sheets are book-bound by a book-binding means such as a stapler and are discharged and stacked, and an image forming apparatus having such a stacking apparatus.
More particularly, the present invention relates to a discharged sheet stacking apparatus in which, sheets are temporarily stopped for both-face imaging treatment and stapling treatment, the sheets are discharged, and an image forming apparatus such as a printer, a copying machine and the like, having such a stacking apparatus.
2. Related Background Art
As discharged sheet stacking apparatus for a laser beam printer (image forming apparatus) having a book-binding apparatus such as a stapler, a stacking apparatus which is connected to a side of the printer body including a discharge opening and in which imaged sheets are stapled for each job and are discharged and stacked is well known. However, since such a discharged sheet stacking apparatus has a discharged sheet switch-back mechanism for permitting the imaged sheets to be stapled and stacked in a page sequence, an installation area is increased and, since a sheet-to-sheet distance is increased to ensure the switch-back of the sheet, through-put of print is worsened.
To avoid such inconveniences, there has been proposed a discharged sheet stacking apparatus in which sheets are conveyed in a reverse manner and are stacked on an upper surface of a printer to omit a reversing mechanism. However, in order to stack a large number of sheets in such a discharged sheet stacking apparatus, strength of the printer body for supporting the sheets must be increased, thereby increasing the cost of the printer body.
To avoid such inconvenience, there has been proposed a discharged sheet stacking apparatus of so-called xe2x80x9clower-installedxe2x80x9d type in which a discharged sheet stacking portion is disposed below a printer body, and a flapper (branching means) for feeding sheets to a sheet discharge apparatus arranged below the printer body is provided in a sheet discharge path of the printer body and a convey portion for conveying the sheet downwardly from the flapper to the sheet discharge apparatus is provided out of the printer body, and an actuator for actuating the flapper of the printer body is provided in the convey portion, thereby avoiding such inconvenience.
However, in order to effect the book-binding by using the book-binding means such as the stapler, a plurality of sheets must be aligned with each other for each job. Generally, in a conventional aligning means, a sheet aligning portion is inclined with respect to a horizontal plane by about 10xc2x0 to 30xc2x0 so that the sheets are aligned with each other by abutting the sheets against a vertical wall portion provided at an inclined end by utilizing the inclination of the sheet aligning portion.
When the aligning means having the inclined surface is used at the sheet stacking portion in this way, a height of the discharged sheet stacking apparatus becomes great, so that, when the discharged sheet stacking apparatus is installed below the printer as mentioned above, the entire height of the printer is increased. As a result, it will be difficult for the user to handle the uppermost printer.
Further, a sheet bundle stapling mechanism used with the conventional discharged sheet stacking apparatus is designed so that a stapling mechanism portion is shifted along a sheet bundle comprised of sheets aligned with each other on a sheet stacking tray (sheet stacking portion) to staple any position(s) of the sheet bundle. That is to say, in the sheet bundle stapling mechanism provided in the image forming apparatus, after a predetermined number of sheets on which toner images were recorded in an image forming portion are conveyed onto the sheet stacking tray and are aligned there, the stapling mechanism portion is shifted to the predetermined position at the end portion of the aligned sheet bundle on the sheet stacking tray to effect the stapling operation.
However, in the above-mentioned conventional sheet bundle stapling mechanism, the stapling mechanism portion must be shifted by distances corresponding to various sizes of various sheets in order to staple any position on the end portion of the sheet bundle.
Thus, the sheet bundle stapling mechanism becomes complicated, and, since the stapling mechanism portion is shifted, the possibility of occurrence of malfunction will be increased. Further, since a space through which the stapling mechanism portion is shifted must be reserved, it is difficult to make the apparatus compact.
Accordingly, it is difficult to manufacture the conventional sheet bundle stapling mechanism with cheap cost, and a greater installation area for the image forming apparatus having the discharged sheet stacking apparatus is required.
Further, in some sheet bundle stapling mechanisms of the conventional discharged sheet stacking apparatus, the stapling treatment is effected by temporarily stopping or waiting the sheet in the sheet convey path.
The sheet conveyed through a vertical convey portion is received in the discharged sheet stacking apparatus by a pair of align and convey-in rollers and is guided onto an align table (sheet stacking portion). The sheets abut against a tip end stopper portion of a sheet stopper to be stacked on the align table.
When a predetermined number of sheets are stacked on the align table as a sheet bundle, the sheets are aligned with each other in a feeding direction and in a direction perpendicular to the feeding direction and then are pinched by a pair of bundle convey rollers (sheet convey rollers). When the convey path is released by rotating the tip end stopper portion in a retard direction, the sheets are conveyed and discharged from the discharged sheet stacking apparatus in the form of the sheet bundle.
In the above-mentioned discharged sheet stacking apparatus, in order to make the apparatus itself simpler and to achieve reduction of cost, a lower bundle convey roller among the pair of bundle convey rollers does not include a drive connection/disconnection means such as a clutch.
Thus, the lower bundle convey roller continues to rotate while supporting (from the below) the sheets urged against the tip end stopper portion. Further, the lower bundle convey roller is positioned substantially flush with an upper surface of the align table to bundle-convey the sheets.
In this way, since the lower bundle convey roller continues to rotate at the position substantially flush with the upper surface of the align table, the roller continues to rub a lowermost sheet in the sheet bundle urged against the tip end stopper portion.
Therefore, the conventional discharged sheet stacking apparatuses have the disadvantages that the surface of the sheet is damaged and the image formed on each sheet is distorted to damage the image.
An object of the present invention is to provide a discharged sheet stacking apparatus and an image forming apparatus, in which the above-mentioned conventional drawbacks can be eliminated and which have a small height.
To achieve the above object, according to the present invention, there is provided a discharged sheet stacking apparatus characterized in that a sheet feed-in means for pinching and feeding-in a sheet onto a sheet stacking portion on which a plurality of sheets are stacked and for causing a tip end of the sheet to abut against a sheet stopper retractable with respect to the sheet stacking portion is disposed at a position spaced apart from the sheet stopper by a distance smaller than a length of the sheet, and the sheet feed-in means continues the feed-in operation while pinching a tail end of the sheet even after the tip end of the sheet abuts against the sheet stopper so that after a loop is formed in the tail end the sheet is stacked onto the sheet stacking portion.
The discharged sheet stacking apparatus may include a sheet auxiliary convey means for conveying the sheet on the sheet feed-in means auxiliary provided between the sheet feed-in means and the sheet stopper.
The sheet auxiliary convey means may comprise an endless belt rotated in a sheet conveying direction.
The discharged sheet stacking apparatus may include biasing means for biasing the tail end of the sheet fed-in by the sheet feed-in means toward the conveying direction.
The biasing means may comprise an endless belt rotated in synchronous with the sheet feed-in means.
The endless belt may be designed so that it drops the sheet while receiving the tail end of the sheet in a condition that the tip end of the sheet abuts against the sheet stopper.
The discharged sheet stacking apparatus may include a staple unit for stapling the sheets stacked on the sheet stacking portion.
Further, the present invention provides an image forming apparatus in which the above-mentioned discharged sheet stacking apparatus is positioned at a lower portion of a main body including an image forming portion for forming an image.
Another object of the present invention is to provide a discharged sheet stacking apparatus which can eliminate the above-mentioned conventional drawbacks and in which a stapling mechanism portion is simplified to minimize malfunction of the stapling mechanism portion.
To achieve this object, according to the present invention, there is provided a discharged sheet stacking apparatus comprising a sheet stacking portion on which fed-in sheets are stacked, and a stapling mechanism portion for aligning ends of the sheets fed-in to the sheet stacking portion to form a sheet bundle and for stapling the sheet bundle, and wherein it further comprises a sheet stopper adapted to align the ends of the sheets conveyed to the sheet stacking portion and retractable with respect to the sheet stacking portion, an aligning member for aligning the sheet in a sheet width-wise direction, a convey means for pinching the sheet bundle from above and below and for conveying the sheet bundle in which the sheets are aligned in the sheet width-wise direction and the ends of the sheets are aligned by the sheet stopper, and a control means for shifting the sheet bundle to a stapling position where the sheet bundle is stapled by the stapling mechanism portion, after the sheet stopper is retracted in response to a stapling mode.
The discharged sheet stacking apparatus may include a drive means for shifting the aligning member, a detecting means for detecting the fact that the sheet is conveyed to the sheet stacking portion, and the control means may control the drive means in such a manner that the aligning member is shifted to an align position whenever the detecting means detects the fact that the sheet is conveyed to the sheet stacking portion, and, when the sheet bundle is conveyed after all of the sheets are stacked on the sheet stacking portion, the aligning member is shifted to a convey position.
Further, according to the present invention, the aligning member may include an elastic member for urging the sheets elastically.
A further object of the present invention is to provide a discharged sheet stacking apparatus and an image forming apparatus having such a discharged sheet stacking apparatus, which can eliminate the above-mentioned conventional drawbacks and in which a surface of a sheet is not damaged and an image formed on the sheet is not damaged.
To achieve this object, according to the present invention, there is provided a discharged sheet stacking apparatus comprising a sheet stacking portion on which a plurality of sheets can be stacked, a storing means for storing the sheets on the sheet stacking portion, and a pair of sheet convey rollers for pinching and discharging the sheets on the sheet stacking portion, and wherein one of the pair of sheet convey rollers is positioned near the sheet stacking portion and the other rollers can be engaged by and disengaged from the one roller from the above, and further wherein it further comprises a sheet receiving member disposed above the one roller and adapted to support the sheets on the sheet stacking portion and to be retarded to contact the sheet with the one roller when the storing means releases the storing of the sheets and the other roller is lowered.
The storing means may comprise a sheet stopper retractable with respect to the sheet stacking portion and adapted to receive the sheets, and the sheet receiving member may comprise a rotatable link piece operated in synchronous with the sheet stopper. The link piece is protruded above the one roller when the sheet stopper is protruded above the sheet stacking portion and is retarded when the sheet stopper is retracted into the sheet stacking portion.
The sheet receiving member may comprise a link piece rotatingly biased by an elastic body toward a direction for protruding the link piece above the one roller, which link piece is retarded by being urged by the other roller being lowered.
The sheet receiving member may comprise a rotary cover rotatably provided coaxial with the one roller and rotatingly biased by an elastic body toward a direction for protruding the rotary cover above the one roller, which rotary cover is rotatingly retarded by being contacted with the other roller being lowered.
The above-mentioned conventional drawbacks can be eliminated by an image forming apparatus according to the present invention comprising an image forming portion for forming an image and the above-mentioned discharged sheet stacking apparatus.